Method and System for Implementing Inter-Access Networks Handoff in Active State in HRPD Network

ABSTRACT

A method and system for implementing an inter-Access Network (AN) handoff in an active state in a High Rate Packet Data (HRPD) Network are disclosed. The method includes determining that an inter-AN handoff operation is necessary and initiating a handoff procedure to perform the inter-AN handoff, sending data to be transmitted to an access terminal to the destination AN in advance in the handoff procedure, and then sending the access terminal the data to be transmitted to the access terminal by the source AN or the destination AN according to the result of the handoff procedure.

The present application is a continuation of U.S. application Ser. No.11/941,283, filed Nov. 16, 2007, which is a continuation ofInternational Application No. PCT/CN2006/000989, filed May 16, 2006,which claims priority to Chinese Application No. 200510072595.2, filedMay 16, 2005, Chinese Application No. 200510070971.4, filed May 19,2005, and Chinese Application No. 200510077113.2, filed Jun. 14, 2005,each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to the field of communications, and inparticular, to a method and system for implementing an inter-AccessNetwork (AN) handoff in an active state in a High Rate Packet Data(HRPD) network.

BACKGROUND

With the development of communication technologies, the 3rd GenerationPartnership Project 2 (3GPP2) proposed a standard for HRPD technology inorder to solve the crucial issue on air interfaces in a Code DivisionMultiple Access (CDMA) system. This standard aims to improve the datatransmission rate on a wireless interface. Compared with the data rateof 153.6 kbit/s provided by CDMA 2000 1x, the HRPD technology mayprovide a forward data rate up to 2.4 Mbit/s.

In an HRPD network, a new modulation technique is utilized over airinterface and methods for data rate control, scheduling optimization andtime division multiplex and the like are added, which cause asignificant improvement in data transmission rate over air interface. Inthe HRPD technology, a private data channel on a CDMA carrier (1.25 MHz)may be employed to support high rate packet data services, with aforward data rate up to 2.4576 Mbit/s, and a peak data rate of 153.6kbit/s for a single user supported in reverse direction.

A separate carrier is needed to support HRPD when deploying an HRPDnetwork. In this manner, when moving in the HRPD network, an accessterminal may move from one AN into another AN in the HRPD network. Atthis time, a handoff from a source NA to a destination NA is necessary.

Currently, the 3GPP2 standard supports only the inter-AN handoff indormant state. This handoff process is as follows: when an accessterminal performing a data service in an HRPD network moves to an edgeof the coverage zone of a cell, it is necessary to be handed off toanother AN so as to continue its data service. At this time, the systemswitches the packet data service from an active state to a dormant stateat the source AN, and then hands off to the destination AN in thedormant state. After moving into the destination AN, the system switchesthe packet data service from the dormant state back to the active stateat the destination AN.

With the above handoff process, a handoff operation from a source AN toa destination AN may be implemented. However, for a data service withhigh real-time requirement, such as Voice over IP (VoIP), Video Phone,Push-To-Talk (PTT) and stream media, such a handoff process may cause aninterruption of the service, which will result in an adverse effect tothe utilization of the service for the user.

In other words, in the method of inter-AN, inter-Packet Control Function(PCF) handoff in dormant state provided in the prior art standard, it isnecessary to release the Point-to-Point Protocol (PPP) connection beingin use during a handoff process, and thus it is necessary for a PacketData Service Network (PDSN) to reallocate a new PPP connection for thedestination network. During the reallocation of the new PPP connection,for one thing, the service of the user may be interrupted due to thefailure of the reallocation process resulted from problems of theresources; for another, the current service of the user may be delayedsignificantly because it will cost the PDSN some time to reestablish aPPP connection.

In view of this, a hard handoff process is required to ensure thecontinuity of a service during an inter-AN handoff process. However, inthe prior art standard, only an inter-AN handoff process in dormantstate is defined, and there is a lack of an inter-AN, inter-PCF hardhandoff process in an active state in an HRPD system.

SUMMARY OF THE INVENTION

In view of the above, the present invention is to provide a method andsystem for implementing an inter-AN handoff in an active state in anHRPD network, to ensure the continuity of a service for an accessterminal during a handoff process across ANs, across PCFs.

Based on this, the present invention provides a method to ensure thereturnablity in the case of a failure of a handoff, so as to improve thereliability of the service communication.

The present invention provides the following technical solutions.

A method for implementing an inter-AN handoff in an active state in anHRPD network is provided, which includes the following steps. It isdetermined that an inter-AN handoff operation is necessary, and ahandoff procedure is initiated. In the inter-AN handoff procedure, aconnection between a destination AN and a PDSN is established before anaccess terminal establishes a connection with the destination AN, anduser data is sent by the PDSN to the destination AN/PCF. When the accessterminal establishes a connection with the destination AN, the datareceived from the PDSN is sent from the destination AN/PCF to the accessterminal.

Here, determining that the inter-AN handoff operation is necessary andinitiating the handoff procedure includes the following steps. A sourceAN determines that an inter-AN handoff operation is necessary accordingto a received route update message, and determines the destination ANcorresponding to the source AN. The source AN sends a handoff requestmessage to the destination AN.

Here, when a handoff is performed between Access Networks belonging todifferent PCFs, establishing the connection and sending the user dataincludes the following steps. In response to receiving the handoffrequest sent from the source AN, the destination AN sends a connectionestablish request to the destination PCF, and establishes a connectionbetween the destination PCF and the destination AN; the destination PCFregisters to the PDSN, and establishes a connection between thedestination PCF and the PDSN. When a source PCF requests to stop sendingdata, the PDSN sends data to the destination PCF and stops sending datato the source PCF.

This last step could include the following steps. When disconnecting ofan air interface connection between the source AN and the accessterminal is determined, the source PCF sends a stop-sending-data requestto the PDSN requesting the PDSN to stop sending data the source PCF.When receiving the stop-sending-data request sent from the source PCF,the PDSN starts sending data to the destination PCF if the PDSN has notsent data to the destination PCF, while stopping sending data to thesource PCF.

Here, when a handoff is performed between Access Networks belonging todifferent PCFs, establishing the connection between the destination ANand PDSN and sending the user data includes the following steps. Inresponse to receiving the handoff request sent from the source AN, thedestination AN sends a connection establish request to the destinationPCF, and establishes a connection between the destination PCF and thedestination AN. The destination PCF registers to the PDSN, andestablishes a connection between the destination PCF and the PDSN. Afterthe connection between the destination PCF and the PDSN has beenestablished, the PDSN sends a bi-cast indication message to the sourceAN to notify the source AN/PCF that the PDSN will send data to thedestination PCF/AN and the source AN/PCF simultaneously.

When the existing connection between the PCF and the PDSN is determinedas an inter-AN handoff, the PDSN sends the bi-cast indication message.Here, the data includes real-time service data and non-real-time servicedata. Here, the method further includes in response to receiving thebi-cast Indication message, the source AN stops sending real-timeservice packets while continuing to send non-real-time service packets.

Here, the method further includes that when the access terminal canreceive data via the destination AN, the destination AN sends a handoffcomplete message to the source AN, and that in response to receiving thehandoff complete message, the source AN interchanges information withthe source PCF, and releases the connection between the source PCF andthe source AN.

Here, establishing the connection and sending the user data furtherincludes the following step. The source AN sends a channel assignmentmessage to the access terminal according to a handoff reply message sentfrom the destination AN, and interchanges information with the sourcePCF instructing to disconnect an air interface connection when receivinga reply from the access terminal, or, the source AN interchangesinformation with the source PCF instructing to disconnect the airinterface connection directly after sending the channel assignmentmessage without waiting for the replay from the access terminal.

For example, the source AN sends the channel assignment message to theaccess terminal, the access terminal is handed off to the destinationAN, and the destination AN allocates a Uni-cast Access TerminalIdentifier (UATI) for the access terminal, so as to complete assignmentof the UATI. The destination AN interchanges information with thedestination PCF so as to establish an air interface connection of thedestination AN.

Alternatively, the source AN sends a UATI assignment message to theaccess terminal, and sends the traffic channel assignment message to theaccess terminal when the UATI assignment is completed, and completes thechannel assignment. The destination AN interchanges information with thedestination PCF so as to establish an air interface connection of thedestination AN.

Here, for a handoff between Access Networks belonging to different PCFs,the PDSN sends data to be transmitted to the access terminalsimultaneously to the source PCF to which the source AN belongs and thedestination PCF to which the destination AN belongs.

Here, the data to be transmitted to the access terminal is saved in theBase Transceiver Stations corresponding to the source AN and thedestination AN respectively.

Here, the method further includes that when the handoff procedure fromthe source AN to the destination AN fails, the source AN and the sourcePCF send the access terminal the data to be transmitted to the accessterminal.

The present invention further provides a system for implementing aninter-AN handoff in an active state in an HRPD network, including asource AN, a source PCF, a destination AN, and a destination PCF.

After the source AN initiates an inter-AN handoff procedure, thedestination AN establishes a connection with a PDSN before an accessterminal establishes a connection with the destination AN, and the PDSNsends user data to the destination AN/PCF.

After the access terminal has established the connection with thedestination AN, the destination AN/PCF sends the data received from thePDSN to the access terminal.

Here, when the source PCF requests to stop sending data, the PDSN sendsdata to the destination PCF while stopping sending data to the sourcePCF.

Here, after the connection between the destination PCF and the PDSN hasbeen established, the PDSN sends a bi-cast indication message to thesource AN to notify the source AN/PCF that the PDSN will send data tothe destination PCF/AN and the source AN/PCF simultaneously.

As can be seen from the technical solutions provided in the presentinvention, an inter-AN, inter-PCF hard handoff is achieved. During theprocedure for such a hard handoff, the PDSN sends data to thedestination PCF/AN in advance, so that the data may be sent from thedestination PCF/AN to the access terminal immediately after a connectionbetween the access terminal and the destination AN has been established.Accordingly, the continuity of a service may be improved, and the timedelay and the packet loss due to a time delay may be reduced.

Furthermore, if the handoff fails, the data may be sent to the accessterminal by the source PCF, so that the packet loss resulted from thefailed handoff may be avoided.

Alternatively, after a connection between the destination PCF/AN and thePDSN has been established, the PDSN may send a concurrent indicationmessage to the source PCF/AN, and sends data to the destination PCF andthe source PCF simultaneously when receiving a reply from the sourcePCF/AN, then the destination PCF buffers the data in the handoffprocedure. The source PCF also buffers the data after receiving abi-cast indication message for a future return in the case of a handofffailure. Therefore, the reliability may be improved. The destination ANor PCF may send data to the access terminal immediately after theestablishment of a connection between the access terminal and thedestination AN.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the networking structure ofan HRPD network according to the present invention;

FIG. 2 is a flow chart illustrating an inter-PCF, inter-AN hard handoffin a method according to an embodiment of the present invention; and

FIG. 3 is a flow chart illustrating an inter-PCF, inter-AN hard handoffin a method according to another embodiment of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The essence of the present invention lies in that, respective datainformation is sent to a destination AN in advance during an inter-ANhandoff. The data may be saved on the destination AN, or may be saved ona PCF to which the destination AN belongs, or may be saved on a BaseTransceiver Station (BTS) to which the destination AN corresponds.Therefore, the continuity of a service after the handoff process endsmay be ensured. Meanwhile, the data may be sent to the source AN/PCF,and saved at the source AMN/PCF, or saved on a Base Transceiver Station(BTS) to which the source AN corresponds. In this manner, the continuityof a service may be guaranteed whether the handoff is successful or not.Here, the access terminal may be a Mobile Station (MS) or the like.

The networking structure of an HRPD network is generally shown inFIG. 1. In the HRPD network, an Access Terminal (AT) 110 interworks witha source AN 120 through an air interface AL, the source AN 120interworks with a PCF 130 via interfaces A8 and A9, the PCF 130interworks with a PDSN 140 via interfaces A10 and A11. In this manner,the AT 110 may obtain the data traffic sent from the PDSN 140 via thesource AN 120 and the PCF 130.

In the implementation, an method according to the present inventionmainly includes the following.

When a destination AN establishes an A8 connection with a destinationPCF and the destination PCF establishes an A10 connection with a PDSN(the A10 connection is a connection between a PCF and a PDSN) during aninter-PCF, inter-AN hard handoff process, the PDSN determines on its ownaccord whether to send a bi-cast indication message according as whetherthere exists an A10 connection.

During the inter-PCF handoff, after the A8 and A10 have been establishedbetween the destination AN, the destination PCF and the PDSN, the PDSNsends data to both the source PCF and the destination PCF, so as toreduce the delay and packet loss of the destination AN/PCF. Further, thePDSN notifies the source PCF before sending data, and the destinationAN/PCF may receive the subsequent data when receiving the notification.The source AN/PCF will not send the subsequently received data to theaccess terminal if the handoff is successful, and will continue to sendthe data that are not overtime only when the handoff fails.

Or, a method according to the present invention may include thefollowing.

After sending a traffic channel assignment message to (or receiving aresponse to this message from) an access terminal, a source AN requestsa PDSN to stop sending traffic data to a source PCF and send trafficdata in advance to a destination PCF.

In the above process according to the present invention, the PDSN maydecide according to the service options to send data to the destinationPCF while sending data to the source PCF for a delay-sensitive service.In other words, if the requirement for delay is in accord with apredetermined requirement, after the A8 and A10 has been establishedbetween the destination AN, the destination PCF and the PDSN during aninter-PCF handoff.

Furthermore, in the method according to the present invention, the datareceived by the destination AN may be sent directly to a BTS in thedestination AN for buffering, and the data received by the source AN mayalso be sent to a BTS in the source AN for buffering so as to reducedelay during an inter-AN handoff.

Upon receiving a channel assignment complete message or a UATI completemessage from the access terminal, the destination AN sends data to theaccess terminal immediately.

In the technical solution shown in FIG. 2, after sending the trafficchannel assignment message to the access terminal, the source PCF maychoose to send an Xoff (stop sending data) message to the PDSNrequesting the PDSN to stop sending data so as to save the bandwidth(see step 214). Alternatively, the source PCF may choose not to send theXoff message so as to facilitate the return in the case of a handofffailure.

With the method according to the present invention, the requirement ofthe transmission of a real-time service and a non-real-time service in aHRPD network could be met.

In an actual application, an embodiment of the present inventionprovides a process for an inter-AN hard handoff in the case ofinter-PCF, i.e., a process for an inter-AN hard handoff betweendifferent PCFs, which will be described below.

A process for an Inter-AN/Inter-PCF hard handoff, i.e., an inter-AN hardhandoff between different PCFs, is as shown in FIG. 2 which includes thefollowing steps.

Step 21: An AT sends a source AN a route update message which containsthe information of neighboring area in which the signal is stronger.

Step 22: The source AN determines that a hard handoff is necessaryaccording to the route update message, and sends a destination AN ahandoff request message which contains the information of a sessionrelated with the AT.

Step 23: On receiving the handoff request message, the destination ANverifies the message and authenticates the AT. If the verification ispassed, the destination AN establishes an A8 connection with adestination PCF and starts a timer TA8-Setup. Here, an indicationrequesting the PDSN to send data to the destination PCF in advance maybe added in the message for establishing the A8.

Step 24: On receiving an A9-Setup-A8 message, the destination PCFinitiates an A10 connection establishment to the PDSN, i.e., sends aregistration request message to the PDSN requesting the PDSN to senddata to the destination PCF in advance. A new message may be added tosend the indication.

Step 25: After the A10 connection has been established, the PDSNresponds to the destination PCF by sending an A11 registration replymessage, i.e. an A11-registration Reply message.

Step 26: After the A8 connection has been completed, the destination PCFfeeds back an establishment of A9 and A8 interfaces connection message,i.e., an A9-Connect-A8 message, to the destination AN. The destinationAN then stops the timer TA8-Setup.

Step 27: The PDSN sends a bi-cast Indication message to the source PCFindicating that the data will be sent by PDSN to the destination AN/PCFand the source AN/PCF at the same time.

Step 28: After receiving the bi-cast Indication message, the source PCFsends the bi-cast Indication message to the source AN notifying thesource AN to continue to receive data from the source PCF. Afterreceiving the bi-cast Indication message, the source AN needs tocontinue to send the received non-real-time traffic data to the accessterminal. As for the real-time traffic data, the source AN needs to sendonly the data which is received before the reception of the bi-castIndication message to the access terminal. The source AN will not sendthe data which is received after the reception of the bi-cast Indicationmessage to the access terminal unless the handoff fails.

In other words, after determining that the bi-cast Indication messagehas been received, for the data packets which are received after thereception of the bi-cast Indication message, the source AN will not sendthe real-time traffic data packets to the access terminal, but willcontinue to send the non-real-time traffic data packets to the accessterminal.

In addition, in this step, a reply-to-PDSN mechanism may be chosen, anda reply mechanism may also be added between the PCF and AN, so as toensure the reliability of the signaling transmission.

Step 29: After sending the bi-cast Indication message, the PDSN maydecide whether to send forward data to the destination PCF according tothe attributes of traffic, or may send forward data to the destinationPCF uniformly regardless of the attributes of traffic. The destinationPCF saves the received data and sends the received data to the accessterminal immediately after the destination AN establishes a connectionwith the access terminal.

Step 210: After sending the bi-cast Indication message, the PDSN sendsforward data to the source PCF at the same time. The data may be savedat the source PCF, or may be sent to the source AN and saved at thesource AN.

Step 211: The destination AN sends the source AN a handoff request replymessage which contains the parameters of the channel assigned to thedestination AN and the like.

Step 215: After receiving the handoff request reply message, the sourceAN sends a channel assignment message over the traffic channel to the ATinstructing the AT to perform a handoff to the destination AN.

Step 212: At the same time, the source AN sends the source PCF a messagerequesting the disconnection between the A9 and AL interfaces, i.e. anA9-AL-Disconnected message, instructing the source PCF to stop sendingdata to the source AN. In other words, the source AN will not wait areply to the traffic channel assignment message, but directly sends thesource PCF a message requesting the disconnection between the A9 and ALinterfaces, i.e., an A9-AL-Disconnected message, instructing the sourcePCF to stop sending data to the source AN.

Alternatively, after receiving a reply to the traffic channel assignmentmessage, the source AN sends the source PCF a message requesting thedisconnection between the A9 and AL interfaces, i.e., anA9-AL-Disconnected message, instructing the source PCF to stop sendingdata to the source AN.

Step 213: In response to the message requesting the disconnectionbetween the A9 and AL interfaces, the source PCF sends the source AN anacknowledge message, i.e., an A9-A1-Disconnected Ack message, and stopssending data to the source AN.

Step 214: The source PCF sends the PDSN an Xoff message, i.e., a stopsending data message, requesting the PDSN to stop sending data to thesource PCF, and indicating the handoff has been performed.

This step is optional. If this message is sent, the communicationresources of the A interface may be saved. If this message is not sent,it may be ensured not to loss data in the case of a failure of thehandoff though the communication resources of the A interface may beoccupied.

Step 216: When being handed off to the destination AN, the AT sends achannel assignment complete message to the destination AN.

Step 217: The destination AN sends a UATI assignment message to the ATover the traffic channel, to allocate a new UATI for the AT.

Step 218: Upon receipt, the AT sends a UATI complete message back to thedestination AN over the traffic channel.

Step 219: After the handoff is successful, a session between the AT andthe PDSN is activated, and the destination AN sends data to the AT.

This step may be executed at any moment after the execution of step 218,the sooner, the better.

Step 220: The destination AN sends an A9-AL Connected message indicatingthe channel has been activated.

Step 221: The destination PCF sends a registration message, i.e. anA11-Registration Request message, to the PDSN, indicating that the linkhas been activated, and the PDSN sends a registration reply back to thedestination PCF.

If step 214 is not executed or the Xoff message is lost, the PDSN willstop sending data to the source AN/PCF at this moment.

Step 222: The destination PCF sends back an acknowledge message of theconnection between the A9 and the AL, i.e. an A9-AL-Connected Ackmessage, to the destination AN.

Step 223: The destination AN sends a handoff complete message to thesource AN.

Step 224: After receiving the handoff complete message, the source ANsends an A9-Release-A8 message to the source PCF notifying the sourcePCF to release the connection between the A9 and A8 interfaces. At thesame time, a timer TAre19 is started, and the A8 link is released at thesource AN.

Step 225: After receiving the A9-Release-A8 message from the source AN,the source PCF sends an A11-Registration Request message to the PDSN torelease the A10 connection. After releasing the A10 connection, the PDSNsends back an A11-Registration Reply message to the source PCF, and thesource PCF releases the resources of the A10 connection.

Step 226: The source CF releases the resources of the A8 connection, andsends the source AN an A9-Release-A8 Complete message (indicating thatthe connection between the A9 and A8 has been released), and the sourceAN will stop the timer TAre19 on receiving the message.

Steps 215, 216, 217 and 218 described above with reference to FIG. 2 mayalternatively be implemented by the following steps.

After step 211 described above, step 215′ may be executed.

Step 215′: The source AN sends a UATI assignment message to the AT overthe traffic channel to allocate a new UATI to the AT. This new UATI isallocated by the destination AN, and may be carried to the source AN viaa handoff request reply message.

Step 216′: The AT sends a UATI complete message back to the source ANover the traffic channel.

Step 217′: The source AN sends a channel assignment message to the ATover the traffic channel, so as to perform the handoff to thedestination AN.

The step 212 may be executed directly subsequent to step 217′, or may beexecuted after receiving a channel assignment reply message returnedfrom the AT.

After step 214, step 218′ will be executed.

Step 218′: After being handed off to the destination AN, the AT sends achannel assignment complete message to the destination AN over theaccess channel.

In an actual application, the above two processes may be chosen asrequired.

The present invention provides another process for an Inter-AN/Inter-PCFhard handoff as shown in FIG. 3 which includes the following steps.

Step 31: An AT sends a source AN a route update message which containsthe information of neighboring area in which the signal is stronger.

Step 32: The source AN determines that a hard handoff is necessaryaccording to the route update message, and sends a destination AN ahandoff request message which contains the information of a sessionrelated with the AT.

Step 33: On receiving the handoff request message, the destination ANverifies the message and authenticates the AT. If the verification ispassed, the destination AN establishes an A8 connection with adestination PCF and starts a timer TA8-Setup.

Step 34: On receiving an A9-Setup-A8 message, the destination PCFinitiates an A10 connection establishment to the PDSN, in other words,sends a registration message to the PDSN.

Step 35: After the A10 connection has been established, the PDSNresponds to the destination PCF by sending an A11-registration Replymessage.

Step 36: After the A8 connection is completed, the destination PCF feedsback an A9-Connect-A8 message to the destination AN. The destination ANthen stops the timer TA8-Setup.

Step 37: The destination AN sends the source AN a handoff request replymessage which contains the parameters of the channel assigned to thedestination AN and the like.

After receiving the handoff request reply message, the source ANexecutes step 312 to assign the traffic channel. At the same time, step38 is executed to release the connection between the A9 and AL. Ofcourse, step 38 may also be executed after receiving a channelassignment reply message returned from the AT.

Step 38: The source AN sends an A9-AL-Disconnected message (disconnectthe connection between the A9 and AL) to the source PCF, notifying thesource PCF to stop sending data to the source AN.

Step 39: The source PCF returns an A9-AL-Disconnected Ack (acknowledgingthe disconnection between the A9 and AL) message to the source AN, andstops sending data to the source AN.

Step 310: The source PCF sends the PDSN an Xoff message, i.e., a stopsending data message, requesting the PDSN to stop sending data to thesource PCF, and indicating the handoff has been performed.

Step 311: After receiving the message, the PDSN stops sending data tothe source AN, and sends data to the destination PCF, wherein the datamay be sent to the destination AN.

Step 312: The source AN sends a channel assignment message to the ATover the traffic channel, instructing the AT to be handed off to thedestination AN.

The AT may return a reply of this message to the source AN to confirmthe completion of the assignment. However, this operation of returning areply by the AT is optional, and is not a necessary step.

Step 313: When being handed off to the destination AN, the AT sends achannel assignment complete message to the destination AN over theaccess channel.

Step 314: The destination AN sends an UATI assignment message to the ATover the access channel, to allocate a new UATI for the AT.

Step 315: Upon receipt, the AT sends an UATI complete message back tothe destination AN over the traffic channel.

Step 316: After the handoff is successful, a session between the AT suchas a mobile terminal (MS) and the PDSN is activated. That is, the accessterminal may receive data via the destination AN.

This step may be executed at any moment after the execution of step 314,the sooner, the better.

Step 317: The destination AN sends the destination PCF a message toestablish a connection between the A9 and AL interfaces, i.e., an A9-ALConnected message indicating the channel has been activated.

Step 318: The destination PCF sends an A11-Registration Request messageto the PDSN, indicating the link has been activated, and the PDSN sendsa registration reply message back to the destination PCF.

Step 319: The destination PCF sends back an A9-AL-Connected Ack message(an acknowledgment to the A9-AL connection) to the destination AN.

Step 320: The destination AN sends a handoff complete message to thesource AN.

Step 321: After receiving the handoff complete message, the source ANsends an A9-Release-A8 message (releasing the connection between the A9and A8) to the source PCF, and starts a timer TAre19 locally, andreleases the A8 link.

Step 322: After receiving the A9-Release-A8 message from the source AN,the source PCF sends an A11-Registration Request message to the PDSNrequesting to release the A10 connection. After releasing the A10connection, the PDSN sends back an A11-Registration Reply message to thesource PCF, and the source PCF releases the resources of the A10connection.

Step 323: After releasing the resources of the A8 connection, the sourcePCF sends the source AN an A9-Release-A8 Complete message (indicatingthat the connection between the A9 and A8 has been released), and thesource AN stops the timer TAre19.

Steps 312, 313, 314 and 315 described above with reference to FIG. 3 mayalternatively be implemented by the following steps.

After step 37 described above, step 312′ may be executed.

Step 312′: The source AN sends an UATI assignment message to the AT overthe traffic channel to allocate a new UATI to the AT. This new UATI isallocated by the destination AN, and may be carried to the source AN viaa handoff request reply message.

Step 313′: The AT sends an UATI assignment complete message back to thesource AN over the traffic channel.

Step 314′: The source AN sends a channel assignment message to the ATover the traffic channel, so as to perform the handoff to thedestination AN.

Step 38 may be executed directly subsequent to step 314′, or may beexecuted after receiving a channel assignment reply message returnedfrom the AT.

After step 38, step 315′ will be executed.

Step 315′: After being handed off to the destination AN, the AT sends achannel assignment complete message to the destination AN over theaccess channel.

In an actual application, the above two processes may be chosen asrequired.

The steps shown in FIG. 2 and FIG. 3 should not be limited to the exactorder for execution described above, and some of the steps may beexecuted at a time according to actual requirement. For example, step222 in FIG. 2 and step 319 in FIG. 3 need only to be executed after thechannel and UATI assignment for the AT has been completed, and are notlimited to be executed after the connection between A9 and AL isestablished. For another example, the channel and UATI assignment asshown in FIG. 2 and FIG. 3 may be executed at any time afteracknowledging that a connection between the destination AN and PDSN hasbeen established, and is not necessarily be limited to the processingorder as shown in FIG. 2 and FIG. 3.

In summary, with the method according to the embodiments of the presentinvention, an inter-PCF, inter-AN hard handoff may be implemented, and ahandoff mechanism in an HRPD network with less packet loss and higherreliability is provided.

Further, as can be seen from the above description of the methodaccording to the embodiments of the present invention, a system for aninter-AN handoff in an active state in an HRPD network is also provided.The system includes a source AN, a source PCF, a destination AN, adestination PCF and a PDSN. After the source AN initiates an inter-ANhandoff, and before the access terminal establishes a connection withthe destination AN, the destination AN establishes a connection with thePDSN, and the PDSN sends user data to the destination AN/PCF. When theaccess terminal establishes a connection with the destination AN, thedestination AN/PCF sends the data received from the PDSN to the accessterminal.

Here, the PDSN sends data to the destination PCF and stops sending datato the source PCF when the source PCF requests the PSDN to stop sendingdata. Or, after the connection between the destination PCF and the PDSNhas been established, the PDSN sends a bi-cast Indication message to thesource AN notifying the source AN/PCF that the PDSN will send data tothe destination PCF/AN and the source AN/PCF at the same time.

The present invention has been described and illustrated by theembodiments of the present invention and the drawings. It shall berecognized by those skilled in the art that those embodiments anddrawings are merely illustrative and not restrictive, that the presentinvention shall not be limited to those embodiments and drawings andthat various modifications and variations can be made to the embodimentsof the present invention in light of the descriptions and the drawingswithout departing from the spirit and scope of the present invention asdefined by the accompanying claims.

1. A method for implementing an inter-Access Network (AN) handoff in anactive state in a High Rate Packet Data (HRPD) network, the methodcomprising: during a handoff procedure from a source AN to a destinationAN, initiating, by the destination AN, a connection establishmentbetween the destination AN and a Packet Data Service Network (PDSN)before an access terminal establishes a connection with the destinationAN; receiving, by the destination AN or a destination Packet ControlFunction (PCF), data from the PDSN; and after the access terminal hasestablished the connection with the destination AN, sending, by thedestination AN or the destination PCF, the data received from the PDSNto the access terminal.
 2. The method according to claim 1, furthercomprising receiving, by the destination AN, a handoff request messagefrom the source AN.
 3. The method according to claim 2, whereininitiating the connection establishment between the destination AN andthe PDSN before the access terminal establishes the connection with thedestination AN comprises: sending, by the destination AN, a connectionestablishment request to the destination PCF, and establishing aconnection between the destination PCF and the destination AN; andregistering, by the destination PCF, to the PDSN, and establishing aconnection between the destination PCF and the PDSN.
 4. The methodaccording to claim 2, wherein the data received by the destination PCFor the destination AN from the PDSN are sent to the source AN or asource PCF simultaneously.
 5. The method according to claim 1, furthercomprising: sending, by the destination AN, a handoff complete messageto the source AN when the access terminal can receive data via thedestination AN, to cause the source AN interchange information with thesource PCF to release the connection between the source PCF and thesource AN.
 6. The method according to claim 2, wherein after receiving,by the destination AN, a handoff request message from the source AN, themethod further comprises: sending, by the destination AN, a handoffreply message to the source AN to make the source AN send a channelassignment message to the access terminal and interchange informationwith a source PCF to disconnect an air interface connection whenreceiving a reply from the access terminal, or, interchange informationwith the source PCF to disconnect the air interface connection directlyafter sending the channel assignment message without waiting for thereply from the access terminal.
 7. The method according to claim 6,wherein after sending, by the destination AN, the handoff reply messageto the source AN to make the source AN send the channel assignmentmessage to the access terminal, the method further comprises:allocating, by the destination AN, a Uni-cast Access Terminal Identifier(UATI), for the access terminal.
 8. The method according to claim 7,wherein the method further comprises: interchanging, by the destinationAN, information with the destination PCF so as to establish an airinterface connection.
 9. A access network (AN), comprising: a firstunit, configured to initiate a connection establishment between the ANand a Packet Data Service Network (PDSN) before an access terminalestablishes a connection with the AN during handoff procedure from asource AN to the AN; a second unit, configured to receive data from thePDSN; and a third unit, configured to send the data received from thePDSN to the access terminal after the access terminal has establishedthe connection with the AN.
 10. The AN according to claim 9, furthercomprising: a fourth unit, configured to receive a handoff requestmessage from the source AN.
 11. The AN according to claim 9, the firstunit is configured to send a connection establishment request to adestination PCF and establish a connection between the destination PCFand the AN to make the destination PCF establish a connection betweenthe destination PCF and the PDSN.
 12. The AN according to claim 10,further comprising: a fifth unit, configured to send a handoff completemessage to the source AN when the access terminal can receive data viathe AN, to make the source AN interchange information with the sourcePCF to release the connection between a source PCF and the source AN.13. The AN according to claim 9, further comprising: a sixth unit,configured to allocate a Uni-cast Access Terminal Identifier (UATI) forthe access terminal.
 14. The AN according to claim 9, furthercomprising: a seventh unit, configured to interchange information with adestination PCF so as to establish an air interface connection.